Hello Prodromos. How are you?
A couple of Google searches (for example) will yield results:
Interventional Radiology UK
http://www.bsir.org/
Interventional orthopedics UK
http://www.interventionalpain.co.uk/faculty.html
This sort of thing: Searching for Interventional Radiology UK, Interventional Orthopaedics UK, Interventional Pain Medicine UK, will give you ideas.
Sorry, but I was stumped when I first read this. Having had time to think about it, something did come to me. In case you have not found anyone yet, maybe you could contact doctors that you have worked with in the UK in the past and ask them for a referral. Or look up the website of the hospital where you were treated for your heart condition (or other hospitals) and see if the hospital has a pain management department. Good luck.
Sorry, I wish I could help but have no clue, I hope one of our members may be able to help.
Best of Luck,
~Tuck